JPH10158728A - Electric heating method - Google Patents

Abstract

(57) [Problem] To provide an electric heating method capable of suppressing power loss in a power transmission material and heating with high heating efficiency when directly heating a metal material having a relatively large cross-sectional area such as a metal bar. provide. An energization heating method in which electrodes are brought into contact with both ends of a metal material as a material to be heated and energized, and heating is performed using Joule heat of the material to be heated, wherein the metal material (1)
Electrodes (2) having two or more and contacting their ends
A series metal material is formed by electrically connecting in series with a power transmission material (7) via the power supply material, and both ends (5a) and (5b) of the metal material electrically connected in series are close to the power supply. An electric heating method comprising: disposing an electrode at both ends thereof, and shortening a power transmission path for supplying power from a power source via a power transmission material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric heating method in which an electrode is brought into contact with a metal material such as a metal rod, a metal tube, a metal thick plate or the like to energize and heat.

[0002]

2. Description of the Related Art Conventionally, as a method for heating a metal material such as a metal bar, an induction heating method and a direct current heating method have been adopted in addition to a method using a heating furnace. In the method using a heating furnace, the equipment cost is high and the heating rate cannot be increased because of atmospheric heating. Further, induction heating uses high frequency, so that the equipment is complicated and expensive, and the heating efficiency is low. Therefore, in recent years, the use of the direct current heating method has begun to be considered.

FIG. 3 is a view for explaining a method of heating a metal material by directly energizing the metal material disclosed in Japanese Patent Application Laid-Open No. 6-136433.

In this method, when the electrodes 2 are brought into contact with both ends of a metal rod 1 to be heated and energized and heated, an energizing condition for minimizing a heating temperature deviation is determined, and the heating temperature is determined based on the energizing condition. In this method, an electrode contact area, the number of contact electrodes, and energizing conditions for minimizing the deviation are determined in advance, and the material to be heated is uniformly heated over the entire length by heating under the energizing conditions.

In the above-described method for heating the metal bar or the like, the power is supplied from the power source 4 to the metal bar 1 to be heated through the power transmitting material 3 and the electrode 2 to heat the metal bar 1. Usually, the current-carrying material 3 and the electrode 2 are made of copper or a copper alloy having a small specific electric resistance.

Since the voltage applied to the power transmission member 3, the electrode 2, and the metal bar 1 is proportional to the respective electrical resistances, the voltage from the power source 4 is efficiently applied to the metal bar 1, and the power transmission member 3 and the electrode 2, the power loss due to the resistance heating is small.

However, the metal bar 1 which is the material to be heated is
Is large, the electrical resistance of the metal bar 1 is small, and the ratio of the resistance to the power transmission material 3 is relatively small. For this reason, the ratio of the voltage applied to the power transmission material 3 increases, and in order to perform heating in the same time as the small cross-section material,
Since it is necessary to increase the current in proportion to the increase in the cross-sectional area, the power loss due to the resistance heating in the power transmission material 3 increases, and the heating efficiency decreases.

As a countermeasure, a method of increasing the sectional area of the power transmission material 3 to reduce the electric resistance can be considered. However, problems such as an increase in size of the equipment and difficulty in handling occur. In particular, when the material to be heated is a metal material having a large cross-sectional area, such as a thick steel plate such as a slab or a thick large-diameter pipe, this effect is large.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem which has conventionally been a problem when directly heating a metal material having a relatively large cross-sectional area, such as a metal bar or a thick-walled tube. Another object of the present invention is to provide a current-carrying heating method capable of heating with high heating efficiency.

[0010]

Means for Solving the Problems The present inventors have conducted an experimental study on a method for suppressing power loss due to resistance heating in a power transmission material during energizing heating of a metal material having a large cross-sectional area, and have obtained the following findings. . a) The length of the power transmission material used between the power source and the electrode to be brought into contact with the material to be heated should be as short as possible.

B) To this end, the number of materials to be heated is two or more, the ends of the materials to be heated are connected in series by a power transmitting material, and both ends of the material to be heated connected by the power transmitting material are brought close to a power source. I just need.

The present invention has been made based on such knowledge, and the gist of the invention is that “electrodes are brought into contact with both ends of a metal material to be heated, and electricity is applied to use the Joule heat of the material to be heated. An electric heating method for heating, and forming a series metal material by electrically connecting two or more metal materials in series with a power transmission material through electrodes in contact with their ends, A power supply having a shortened power transmission path, characterized in that both ends of a metal material electrically connected in series are arranged so as to be close to a power supply, and electrodes are brought into contact with both ends thereof and power is supplied from the power supply via a power transmission material. Heating method ".

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The metal material to be heated which is the object of the electric heating method of the present invention may be a metal material which generates Joule heat by energization and is heated. Generally, carbon steel, low alloy steel, stainless steel Steel etc. are raised.

The shape of the metal material to be heated is not particularly limited. The shape of the metal material to be heated can be applied to metal materials such as rod-shaped materials, tubular materials, and plate-shaped materials. Effective for large materials. In the following description, a metal bar is described as an example.

FIG. 1 is a conceptual diagram for explaining an energization heating method of the present invention in a case where metal rods to be heated are connected in series by a power transmission material, wherein (a), (b), and ( c) is an example in which the number of materials to be heated is two, three, and four, respectively.

As shown in FIGS. 1A to 1C, in this energization heating method, two or more metal bars 1 are energized and heated at the same time. Is electrode 2
And are electrically connected in series by short power transmitting members 6 and 7.

That is, in this energization heating method, most of the current path from the power supply is made of the metal material to be heated, so that the length of the power transmission material per material to be heated is longer than that of the conventional method shown in FIG. That is, the power transmission path can be significantly reduced. Since the electrical resistance over the entire length of the power transmission material can be reduced, the voltage from the power source is efficiently applied to the metal bar,
Power loss due to resistance heat generation in the power transmission material can be greatly reduced, and heating efficiency can be improved.

The reason why the number of the metal materials to be heated is two or more is that the end of the metal material to be heated to be brought into contact with the electrode is arranged close to the power source.

That is, by using two or more materials to be heated, the materials to be heated can be arranged as shown in FIGS. 1 (a) to 1 (c).
a, 5b can be brought closer to the power supply 4. As described above, by simultaneously heating a plurality of metal materials to be heated, the electric heating method of the present invention can be applied.

Considering the transfer of the material to be heated before and after heating, the handling of the equipment, and the installation space of the electric heating equipment, FIG.
It is preferable that the number of materials to be heated be an even number so that the materials to be heated are arranged side by side in the same direction as in (a) and (c).

In order to make the current density in all the connected metal bars 1 uniform and to achieve the same heating conditions, it is preferable that the cross-sectional areas of all the metal bars 1 are the same. Regarding the length of the metal bar 1, even if the length of each connected metal bar 1 is different, the moving mechanism of the electrode 2, the power transmission material 6,
Application is possible if the length of 7 is considered. However, in order to reduce the power loss in the power transmission members 6 and 7 as much as possible, it is preferable that the length of the metal bars 1 to be simultaneously heated is the same and the length of the power transmission members 6 and 7 is as short as possible.

In the conventional electric heating method shown in FIG.
As the length of the metal bar 1 increases, the length of the power transmission material also needs to be increased, and the power loss in the power transmission material 3 also increases. But,
In the electric heating method of the present invention, since the length of the power transmission members 6 and 7 can be constant regardless of the length of the metal bar 1, the power loss in the power transmission members 6 and 7 is reduced by the metal bar. It can be minimized regardless of the length of one.

Either a DC power supply or an AC power supply may be used as the power supply 4. When an AC power supply is used, for example, the current paths (in the directions shown in FIGS. In the case of the electric heating method of the present invention, the power factor at the time of applying an alternating current can be improved by arranging the metal rod 1 that forms the majority of the current path in close proximity.

FIG. 2 is a diagram for explaining another embodiment of the electric heating method.

In this method, two or more sets of metal bars electrically connected in parallel by the power transmitting material 7 via the electrode 2 are electrically connected in series by the power transmitting material 7a. Even with such an electric heating method, it is possible to shorten the length of the power transmission material as compared with the conventional electric heating method. This method is applicable if the number of metal bars is even.
However, as the number of metal bars connected in parallel increases, the electric resistance of the entire metal bars connected in parallel decreases, and the ratio of the voltage load from the power supply decreases. The effect of improving the heating efficiency is smaller than in the case. In this case, by increasing the number of sets of parallel metal bars connected in series, the electric resistance of the entire metal bar can be increased and the heating efficiency can be improved, but a large number of metal plate bars are heated at a time. It is not preferable because it is necessary and the arrangement of the power transmission material is complicated.

[0026]

EXAMPLE Two metal bars of S45C were connected in series with an electrode and a power transmitting material as shown in FIG. 1 (a) and heated by energization, and the power loss in all the power transmitting materials was determined.

The dimensions of the material to be heated, the electrode and the power transmission material were as follows.

Metal bar dimensions Diameter: 212 mm, length: 3000 mm Electrode (copper) Diameter: 200 mm, length: 100 mm Power transmission material 6 (copper busbar) Width: 100 mm, thickness: 20 mm, length: 750 mm Power transmission material 7 (copper bus bar) width: 100 mm, thickness: 20 mm, length: using 500mm copper bus bars one by each four, and the cross-sectional area of the power transmission member for a total 8000mm ^2. The power supply 4 has a power capacity 3
A 000 kW DC power supply was used.

Next, as a conventional example, heating was also performed by the electric heating method shown in FIG. S4 of the same dimensions as above
Using a 5C metal bar, the power transmission material 3 has a width of 100 mm,
Four copper bus bars each having a thickness of 20 mm and a length of 2500 mm were used.

The electrical resistance of all metal bars and all power transmitting materials used in the method of the present invention and the conventional method was measured, and the ratio of the electrical resistance of all power transmitting materials to all metal bars was determined. Table 1 shows the results.

[0031]

[Table 1]

As is apparent from Table 1, the electric resistance of the transmission material to the metal bar can be greatly reduced by the electric heating method of the present invention.

With respect to heating conditions, in the conventional method, one metal bar was heated from normal temperature to 1000 ° C. for 5 minutes.

In the method of the present invention, in order to heat two metal bars at the same time, they were heated from room temperature to 1000 ° C. for 10 minutes. At the time of heating, in order to suppress heat dissipation from the metal bar 1, the metal bar 1 was heated in a cover made of a heat insulating material such as a firebrick or a wall.

Table 2 shows the results of measuring the voltage, current, and electric power of the power supply, the metal rod, and the transmission material when the electric heating was performed by the method of the present invention and the conventional method under such heating conditions. Table 2 also shows the results of the power loss and the heating efficiency of all the power transmission materials.

[0036]

[Table 2]

As shown in Table 2, the power loss in the transmission material is greatly reduced by the electric heating method of the present invention as compared with the conventional method, and the heating efficiency is about 67% in the conventional method.
On the other hand, in the method of the present invention, it was improved to about 81%.

[0038]

According to the electric heating method of the present invention, it is possible to greatly reduce the power loss due to the resistance heating in the power transmission material and to obtain a high heating efficiency.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an example of an electric heating method according to the present invention.

FIG. 2 is a diagram showing another embodiment of the electric heating method of the present invention.

FIG. 3 is a diagram showing a conventional energization heating method.

[Brief description of reference numerals]

 1: Metal bar 2: Electrode 3, 6, 7, 7a: Power transmission material 4: Power supply

Claims (1)

[Claims] An electric heating method in which an electrode is brought into contact with both ends of a metal material to be heated and an electric current is applied thereto, and heating is performed using Joule heat of the material to be heated. Forming a series metal material by electrically connecting the materials in series with the power transmission material through the electrodes in contact with their ends,
A power supply having a shortened power transmission path, characterized in that both ends of a metal material electrically connected in series are arranged so as to be close to a power supply, and electrodes are brought into contact with both ends thereof and power is supplied from the power supply via a power transmission material. Heating method.